Colorectal cancer (CRC) is the second most common cause of cancer deaths, despite being preventable by removing precancerous colon polyps. Therefore, polyp detection rates are a critical measure of endoscopist performance quality. After polyp removal, endoscopists depend on national guidelines to provide evidence- based recommendations for appropriate intervals between colonoscopies. Serrated polyps include hyperplastic polyps (HPs) and sessile serrated polyps (SSPs). Recent evidence indicates that a subset of serrated polyps are important precursors to CRC, highlighting the need for evidence to clarify optimal detection and follow up of serrated lesions. Long-term outcome data to support specific surveillance guidelines in patients with serrated polyps is lacking. Current screening guidelines consider patients with only small HPs in the recto-sigmoid to be at average-risk, and recommend a 10 year return interval. Patients with SSPs are thought to be at higher risk, and shorter return intervals are suggested, based on limited evidence. However, even expert pathologists differ as to whether some polyps are HPs or SSPs, and it remains unclear whether proximally located polyps designated as HPs should be considered SSPs, with accordingly higher risk and shorter surveillance intervals. The New Hampshire Colonoscopy Registry (NHCR), a statewide population-based registry, is uniquely able to provide the long-term outcome data needed to move this developing field forward. Comprehensive data on endoscopist polyp detection rates will identify sources of variation in serrated polyp detection. By 2017, 13,000 NHCR patients will surpass the critical 10 year follow-up interval recommended for patients with normal exams or only small HPs. Increasing numbers of patients will return for repeat exams, and the NHCR database will contain data on risk factors, colonoscopy characteristics and pathology for 145,000 patients, nearly 13,500 with serrated polyps, allowing research into outcomes following all types of serrated polyps. Specific Aims: 1) To investigate variability in serrated polyp detection rates among the approximately 100 endoscopists participating in the NHCR, exploring factors associated with variable detection rates, including patient, endoscopist, procedure, and endoscopy facility characteristics, and 2) To identify factors associated with an increased risk for advanced outcomes - defined as histologically advanced polyps or CRC - at follow- up colonoscopy in patients with baseline serrated polyps. We will investigate the outcomes for serrated polyp subtypes, according to their baseline size, location in the colon, and number of serrated polyps detected, and also analyze the impact of patient risk factors, baseline colonoscopy characteristics, and other findings (such as concurrent conventional adenomas), on future risk of advanced outcomes. This study aims to provide new high-quality population-based evidence needed to refine and strengthen current surveillance guidelines and quality indicators and thereby improve the effectiveness of screening in preventing CRC.